With everything said, let me sum it up with the following words: "Network of Trust".
Taken from Linus Torvald's mouth during his Git talk in Google back in 2007 (Starts at 27:35):
And I quote:
…the way real security work is done: by Network of Trust. If you have ever done any security work, and it did not involve the concept of Network of Trust, it wasn't security work. It was, Masturbation.
It's the basics of any security work. In that sense, I don't think any
sane admin would give out SSH accounts to anyone not part of their list of trusted people.
It's the same with Hamachi. You create your own network, then
you invite the people you trust to become part of that network.
Everyone raised good points. Security isn't something to be taken lightly. It's probably been stressed more than enough times here.
But let me go back on topic: the OP is asking for ways to reduce lag. And like anything in real life, not all solutions make sense. Some are just happy to have it working (like my SSH workaround). Some are willing to cut corners just to have a great experience. And that's what really matters here.
We've given enough advice on things like security and what to check. Let the user decide on what to do.